Titanium-aluminium (Ti—Al) based alloys and alloys based on titanium-aluminium (Ti—Al) inter-metallic compounds are very valuable materials. However, they can be difficult and expensive to prepare, particularly in a powder form. This expense of preparation limits wide use of these materials, even though they have highly desirable properties for use in aerospace, automotive and other industries.
Reactors and methods for forming titanium-aluminium based alloys and inter-metallic compounds have been disclosed. For example, WO 2007/109847 discloses a stepwise method for the production of titanium-aluminium based alloys and inter-metallic compounds. WO 2007/109847 describes the production of titanium-aluminium based alloys and inter-metallic compounds via a two stage reduction process, based on the reduction of titanium tetrachloride with aluminium. In stage 1, TiCl4 is reduced with Al (optionally in the presence of AlCl3) to produce titanium subchlorides according to the following reaction:TiCl4+(1.333+x)Al→TiCl3+(1+x)Al+0.333AlCl3 TiCl4+(1.333+x)Al→TiCl2+(0.666+x)Al+0.666AlCl3 
In stage 2, the products from stage 1 are processed at temperatures between 200° C. and 1300° C. to produce the titanium-aluminium based alloys or inter-metallic compounds in a powder form, according to the following (simplified) reaction scheme:TiCl3+(1+x)Al→Ti—Alx+AlCl3 TiCl2+(0.666+x)Al→Ti—Alx+0.666AlCl3 
Whilst the reactors and methods disclosed in WO 2007/109847 are useful for producing titanium-aluminides such as γ-TiAl and Ti3Al (which contain a relatively high proportion of aluminium), they have not been able to reliably and consistently produce low-aluminium titanium-aluminium based alloys (i.e. titanium-aluminium based alloys containing less than about 12-15 weight % (12-15 wt. %) aluminium).
WO 2009/129570 discloses a reactor adapted to address one of the problems associated with the reactors and methods disclosed in WO 2007/109847, when such are used under the conditions that would be required to form low-aluminium titanium-aluminium based alloys. In particular, when operating in accordance with the conditions required to form low-aluminium titanium-aluminium based alloys, the reaction materials tend to accrete at a particular temperature, which can clog the reactor and prevent it from continuously operating. The reactor of WO 2009/129570 comprises a removing apparatus, which is operable to remove any accreted materials from an intermediate section of the reactor that is maintained at the temperature at which accretion can occur. The intermediate section may also be adapted such that materials are quickly transferred therethrough in order to minimise the time spent by the material at temperatures at which accretion can occur.
The above references to the background art do not constitute an admission that such art forms a part of the common general knowledge of a person of ordinary skill in the art.